Apparently, plenty of travelers aren’t turned off by airlines that charge extra for everything from paying for flights with a credit card to $3 bottles of water on board the plane. Lately, the most profitable carriers in the U.S. and Europe are the ones that pile on fees at every turn.

The hope among fee-fatigued travelers was that consumers wouldn’t stand for getting nickel-and-dimed by the airlines. The thinking went that once passengers wised up and stopped flying with carriers such as Spirit Airlines, which charge for things like carry-on bags and seating assignments, these airlines would go out of business or be forced to change their fee-happy ways.

Just the opposite appears to be happening.

It’s the airlines that have been reluctant to tack on fees that, after catching wind of the profitability of Spirit and others, are more likely to be changing their ways by copying the more-fees blueprint.

The Wall Street Journal recently pronounced Spirit, the unquestioned leader in travel fees in the U.S., as “pound for pound, the most profitable airline in the U.S.” According to the most recent data, Spirit siphons, on average, $103 per passenger in fees above and beyond the price of a ticket for every round-trip flown. That figure, mind you, was based on charges that have subsequently been jacked up for services such as bringing a carry-on bag aboard the flight—which can now cost as much as $100, up from $45.

While most carriers still allow carry-on bags for free, Allegiant Air recently announced it is following in Spirit’s footprints by instituting a carry-on bag fee. The Associated Press reported that it’s become standard, more or less, for domestic airlines to force families and friends to pay for the privilege of sitting next to each other on the plane. The reason this is so is that the carriers are selling more and more reservations for window and aisle seats, and often, the only spots left for those not willing to cough up for seat assignment fees are in the middle row. The result is that spouses and families are more likely to wind up in different rows—in uncomfortable middle seats, of course.

While many airlines in the U.S. are following the trend set by Spirit, the airline has been mimicking the pattern established by the world’s most overtly fee-crazed carrier, Ryanair. The Ireland-based airline has drawn headlines with plans to charge passengers for everything from in-flight porn to on-board pay toilets, and it currently drives passengers nuts with hefty checked baggage fees and charges of roughly $10 just to buy a flight with a non-affiliated credit card. Spirit has been called the “Ryanair of the U.S.” dating back to 2009, and Spirit executives say that it “flat-out copied” the Ryanair business model.

This model is proving to be quite successful for Spirit (see above) and Ryanair alike, as Ryanair recently announced record profits thanks to higher flight prices, as well as an 11% boost in revenues from fees collected before and during flights.